Oil mist particle density detection method and apparatus utilizing a stable oil coating and a unijunction oscillator circuit



Dec. 17, 1968 N. H. KADlVNlK 3,417,250

OIL MIST PARTICLE DENSITY DETECTION METHOD AND APPARATUS UTILIZING A STABLE OIL COATING AND A UNIJUNCTION OSCILLATOR CIRCUIT Filed April 22, 1965 2 Sheets-Sheet 1 P76; 2, MEMO/a N. H. KADIVNIK 3,417,250 OIL MIST PARTICLE DENSITY DETECTION METHOD AND APPARATUS Dec. 17, 1968 UTILIZING A STABLE OIL COATING AND A UNIJUNCTION OSCILLATOR CIRCUIT 2 Sheets-Sheet 2 Filed April 22. 1965 United States Patent OIL MIST PARTICLE DENSITY DETECTION METHOD AND APPARATUS UTILIZING A STABLE OIL COATING AND A UNIJUNC- TION OSCILLATOR CIRCUIT Norman H. Kadivnik, Morton Grove, Ill., assignor t0 Stewart-Warner Corporation, Chicago, 111., a corporation of Virginia Filed Apr. 22, 1965, Ser. No. 450,155 11 Claims. (Cl. 250-218) ABSTRACT OF THE DISCLOSURE The following specification describes an oil mist detection method and apparatus in which the ratio of oil to air is determined by the light transmitted through the mist between optical surfaces located in the mist and having a stable coating of oil. The stable coating permits the apparatus to be calibrated with reference to a constant condition at the optical surfaces, while a known ratio of oil to air is transmitted, whereafter variation in the ratio can be unambiguously detected.

The detection apparatus comprises a pair of photocell elements one of which is temporarily connected to a known resistance and the light adjusted for selecting the photocell resistance. Each photocell controls a respective temperature stable unijunction oscillator for firing a respective silicon controlled rectifier as long as light of a selected intensity is transmitted to maintain a high and low light level alarm, respectively, turned off. When a high or low light variation exceeding a predetermined magnitude and duration occurs the corresponding oscillator terminates oscillation to operate the respective alarm.

This invention relates in general to the detection of foreign particles in a fluid stream and more particularly to an improved method and apparatus for detecting or ascertaining variations in the relative particle density of an oil mist in an air stream.

Oil mist has received widespread acceptance for use in automatically and continuously lubricating bearings or other devices subject to friction and wear. The-mist is usually generated by evaporating oil into a heated air stream. The air stream carries the oil mist at oil to air ratios ranging, for example, from below .1 oz./hr./c.f.m. to above .8 oz./hr./c.f.m. depending on the bearing needs and at temperatures sometimes over 315 F. The stream passes through suitable conduits to condensation fittings adjacent the bearings, which in turn condense the mist, as the air stream passes through the fittings to provide continuous and even lubrication of the bearings. The continuous and even lubrication enables the mist to be substituted for extremely viscous lubricants, which require periodic manual application, and substantially reduces maintenance costs resulting from hearing breakdown or failure. In addition, other benefits are derived through the reduction of waste lubrication, which serves as a source of product contamination in some areas, and through the reduction in the possibility of impurities or abrasives being introduced to the bearings.

In order to determine if the oil mist to air ratio is being properly maintained, it is necessary to monitor a selected portion of the air stream containing the oil and ascertain if the oil particle density is maintained within predetermined limits. The air stream carrying the oil mist is generally referred to hereinafter as the oil mist air stream.

One method and apparatus for detecting variations in the oil particle density of an oil mist air stream utilized a lamp and photocell located on opposite sides of a con- Cir duit through which the stream passed, together with an appropriate amplifier circuit for the photocell, as disclosed in application Ser. No. 312,767 filed Sept. 30, 1963, by Kadivnik now Patent No. 3,308,300. In the just mentioned application, the light was transmitted perpendicular to the' direction of stream movement for scanning the stream and the light intensity received by the photocell was proportional to the particle density. As described in application Ser. No. 312,579 filed Sept. 30, 1963, by Bjorn now Patent No. 3,268,734, a curtain of mistfree air was maintained between the oil mist air stream and the external surfaces of the photocell and lamp shown in the Kadivnik application to prevent an oil coating from depositing on their surfaces.

The method and apparatus described in the aforementioned applications, therefore, resulted in the problem of maintaining a particle-free air curtain between the lamp and cell and the oil mist air stream. If the curtain failed, contamination of the lamp or cell surfaces by oil rendered previous calibration ineffective. The use of a single photocell section to ascertain both the maximum and minimum limits of desired particle density also affected calibration and limited the range of particle densities that could be effectively monitored.

In addition, light transmission was perpendicular to the direction of stream movement or along the short axis of the conduit. Since large stream volumes cannot be conveniently scanned transverse to the stream movement, the total difference in particle density between two extreme conditions in the short air stream volume between the lamp and cell provided only limited variations in light transmission. This in turn also limited the sensitivity and range of the apparatus disclosed in the aforementioned applications.

The present invention is based on the unique and simple concept that if the lamp or signal generator and the photocell or signal receiver are located in the oil mist air stream, the oil will deposit thereon to form a stabilized coating of substantially constant thickness over the lamp and photocell external surfaces. Once the coating is stabilized, the circuits associated with the cell and lamp may be adjusted or calibrated for the desired particle density. Variations in light intensity transmitted thereafter to the photocell will simply reflect the changes in the oil mist density of the oil mist air stream without being affected by the coating. This simplifies calibration by enabling the photocell to be adjusted to a known standard resistance in the field, since one of the main variables in the oil mist detection apparatus is stabilized.

The light intensity detected by the photocell is dependent on the total number of particles between the lamp and photocell. As the stabilized coating enables the lamp and photocell to be located in the oil mist air stream, without danger that changes in the coating will alter light transmission, the lamp and photocell are immersed in the stream so that the direction of light transmission to the photocell is parallel to the stream movement or the long axis of the conduit. This permits a large volume of the stream to be conveniently scanned and therefore effectively multiplies any difference in particle density per unit volume by a factor dependent on the separation between the lamp and cell. Far greater sensitivity in detecting variations in the ratio of oil to air in the stream from a d sired value is, therefore, achieved by choosing a conveniently large separation between the lamp and cell along the long axis of the conduit. This large separation may be adjusted, as desired, and permits the range of nominal oil to air ratios which may be effectively detected to be extended considerably.

Locating a photocell directly in the oil mist air stream also presents a problem, since the stream temperature may both vary widely and be well above that desired for optimum photocell operation.

To avoid the latter problem, the present invention utilizes a light transmitting rod which is impervious to the usual temperature conditions encountered in the conduit. The rod receives the incident light transmitted from the lamp and in turn transmits the received light to a photocell external to the conduit, where it is conveniently insulated from high and variable temperatures.

While the circuit illustrated in the aforemetnioned applications provides considerable accuracy and sensitivity it is desirable to also improve the reliability of the circuit apparatus together with the sensitivity and range of application of the circuit apparatus.

For the latter purposes the present invention employs a dual section photocell, with each section controlling a respective free running unijunction oscillator. The oscillators in turn control respective silicon-controlled rectifiers for operating indicators or alarms corresponding to minimum and maximum particle density conditions respectively. The minimum and maximum conditions are, therefore, detected independently, while the stability and current gain of the solid state elements provide reliable and sensitive operation.

It is, therefore, one object of the present invention to provide more reliable calibration for apparatus used to detect variations in the ratio of oil particles to air in an oil mist air stream.

It is another object of the present invention to extend the range of nominal oil to air ratios in an oil mist air stream which can be monitored by oil particle detection apparatus for detecting variations from the nominal ratios.

It is another object of the present invention to enable a photocell located external to an oil mist air stream to be utilized for ascertaining the relative oil particle density of the stream.

It is another object of the present invention to provide an improved method for ascertaining relative particle density in a fluid stream.

It is still another object of the present invention to provide separate, more reliable and improved circuits for detecting, respectively, variations exceeding the desired maximum and minimum oil particle densities in an oil mist air stream.

Other objects and features of the present invention will become apparent on examination of the following specification, claims and drawings wherein:

FIG. 1 is a perspective view of conduit section having oil mist detection apparatus arranged according to the principles of the present invention;

FIG. 2 is a view taken generally along the line 22 in FIG. 1 and illustrating the lamp and photocell assemblies in partial section; and

FIG. 3 illustrates the circuit arrangement employed in the present invention.

A conduit section is illustrated in FIG. 1. The section 10 is arranged in any well known manner in tandem with one or more conduits (not shown) through which an oil mist air stream 11 is transmitted, as indicated schematically. The stream is transmitted in the direction of arrow 12 to one or more bearings, and the conduit 10 occupies a position with respect to the bearings calculated to permit accurate detection of the oil mist actually received at the bearings.

Section 10 carries a lamp assembly 14 and a photocell assembly 16. As is best seen in FIG. 2, the lamp assembly 14 comprises a cup-shaped housing 18 seated on a ring 20 and fastened to the outer surface 22 of the section 10. A gasket 21 is seated between the ring 20 and the surface 22 of section 10. The cup-shaped housing 18 has a top wall 24 in which a conventional electrical connector 26 is located. Connector 26 permits a facile connection to be extended from the filament of a lamp 28 to a pair of leads 30 and 32,

The lamp 28 is fixedly suspended adjacent the central longitudinal axis of the section 10 by means of a support element 34. The support element 34 and a glass envelope 36 encircling element 34 and lamp 28 are in turn carried by a sleeve element 38. Sleeve element 38 has a flange seated on ring 20, and extends through an aperture in the wall of the section 10. Both the support element 34 and glass wall 36 pass through sleeve 38 and are secured by epoxy, or otherwise, to the sleeve element 38. A suitable reflecting surface is deposited directly behind the filament of lamp 28 for the purpose of increasing the light intensity transmitted in the direction of arrow 12 toward the photocell assembly 16, when the lamp 28 is lighted. The light reflecting surface may be simple light reflecting tape 39 adhesively secured to the external wall of lamp 28.

The photocell assembly 16 comprises a transparent cylindrical rod 40 of Pyrex glass, for example, acting as a light or signal receiver. A light transparent flat face 42 is formed in the cylindrical surface adjacent the lower end of the rod and is aligned with lamp 28 along the longitudinal central axis of section 10. A bevel 43 is formed in rod 40 behind face 42 at an angle 45 to the vertical axis 44 of the rod so that the face 42 and bevel 43 act as a prism for reflecting light from lamp 28 along the axis 44. The bevel 43 may be coated with a lightreflecting surface, such as silver, for example, to improve its light reflecting character. Light from lamp 28 is, therefore, transmitted at an intensity dependent on the particle density in stream 11 through the face 42 and is reflected at the bevel 43 along the vertical axis 44. The outer cylindrical surface of the rod is preferably coated for refiecting internally transmitted light and absorbing external light. Such a coating may comprise, for example, a fused platinum coat or a white enamel paint covered successively with a silver and black paint.

The rod 40 passes through an aperture 45 in the wall of section 10 where it is encircled :by a bushing 46 and held therein by a suitable heat insulating and adhesive compound, such as epoxy. Bushing 46 is seated in a heat conductive metal ring 48, which in turn is seated on a gasket 49. Heat insulating standards 50 supported on ring 48 carry another heat conductive ring or heat radiator '52 with rod 40 extending from the section 10 above ring 52 and another group of heat insulating standards 54 on ring 52. The standards 54 in turn carry a ring 56 and a cup-shaped housing 58.

Rod 40 projects into a suitable aperture in ring 56 and a dual section resistance type photocell 60 is suspended from housing 58 directly above the upper end of rod 40 for receiving light transmitted along the axis 44 of rod 40. The photocell is additionally insulated from excessive heat or temperature variations by a fibre washer 64 encircling the end of rod 40 in ring 56 and held in position by a spring 66. A conventional electrical connector 68 is located in the top wall of housing 58 for use in extending electrical connections to the dual section photocell 62 via the leads 70, 72 and 74.

It will be noted that aperture 45 is a slot. The entire assembly 16 including rod 40 may be adjusted longitudinally along conduit 10 by simply loosening nuts 75, which are either aflixed to square headed bolts held in appropriate slotted recesses in conduit 10 or pass through slots in ring 48. The assembly 16 is then moved in the desired direction. The nuts 75 are then tightened to hold the assembly in position. The length of slot 45 is chosen so that it is overlapped by ring 48 in all adjusted positions of assembly 16. The distance between lamp 28 and face 42 of the rod 40 is usually chosen at 7 If the sensitivity is insufiicient at this distance, as may occur with extremely low mist to air ratios, the assembly 16 may be adjusted to provide a greater distance between lamp 28 and rod 40 and thereby enable a greater number of particles to intercept the light.

Lamp 28 and photocell 60 are connected in a circuit arrangement indicated generally at 76 in FIG. 3. The circuit arrangement 76 comprises a transformer T1 having serially connected secondaries S1 and S2 for trans forming, for example, a 60 cycle A.C. supply voltage applied to primary P1 into suitable operating voltages.

One terminal of secondary S1 is connected directly to lead 70, which in turn is connected to opposite terminals of secondary S2 through a resistor R1 and respective rectifiers or unidirectional circuit elements D1 and D2. A similar rectifier D3 and resistor R2 connect the other terminal of secondary S1 to a lead 78, and a filter capacitor C1 is connected from lead 70 to the junction of the rectifier D3 and resistor R2. Secondary S2 has a center tap connected to lead 30 and a filter capacitor C2 is connected between lead 30 and the junction between rectifiers D1 and D2 and resistor R1. In addition, a respective Zener diode Z1 is connected from leads 30 to 70 and a Zener diode Z2 is connected from lead 70 to 78 in order to clamp the voltage on leads 30 and 78 at substantially volts positive and negative, respectively, with respect to lead 70.

Lead is connected to one terminal of lamp 28 and the other terminal of lamp 28 is connected over lead 32 to an adjustable resistor R3. Resistor R3 in turn is connected through resistor R4 to lead 70. The difference in potential between leads 30 and 70 serves to light lamp 28 with the adjustment of resistor R3 controlling the light intensity.

Lead 70 extends to resistors R5 and R6, which are connected to respective base circuits of unijunctions U1 and U2 respectively. Lead 70 also extends to the cathode of a silicon-controlled rectifier SCR1 whose gate circuit is connected between resistor R5 and the associated base circuit of unijunction U1. Lead 70, in addition, is connected to the junction of sections 80 and 82 of the dual section resistance type photocell and to one terminal of a pair of conventional alarm elements A1 and A2.

The other terminal of alarm elements A1 and A2 is connected through respective normally closed contacts 84 and 86 of respective relays 88 and 90 to lead 92. Lead 92 extends to the terminal of secondary S1 opposite to lead so that alarm elements A1 and A2 are operated, unless the respective relays 88 and 90 are also operated to open contacts 84 and 86 respectively.

Relay 88 has a time delay capacitor C3 in shunt therewith, and is connected on one side to the anode of SCR1 and on the other side through a resistor R7 to lead 92. Relay 88 therefore operates whenever SCR1 fires and is held operated for a time, after SCR1 extinguishes, 'by capacitor C3. Relay 90 similarly has a time delay capacitor C4 in shunt therewith and is connected on one side to the anode of a silicon-controlled rectifier SCR2 and on the other side through a resistor R8 to a lead 94 extending to the terminal of secondary 52 connected to rectifier D2. Relay 90 is therefore operated, whenever SCR2 is fired and is held operated for a time, after SCR2 extinguishes, by capacitor C4.

The gate circuit of silicon-controlled rectifier SCR2 is connected between a base circuit of unijunction U2 and a resistor R9. Resistor R9 is connected to lead 30 in common with the cathode of SCR2.

Unijunctions U1 and U2 are connected as free running oscillators with the base current path for U1 extending from lead 78 through resistors R10 and R5 to lead 70. The base current path for unijunction U2 extends from lead 70 through resistors R6 and R9 to lead 30. The emitter circuit of unijunction U1 is connected over lead 72 to the terminal of photocell section 80, opposite lead 70, and a timing capacitor C5 is connected between the emitter and lead 70. The emitter circuit of unijunction U2 is connected over lead '74 to the terminal of photocell section 82, opposite lead 70 and a 300K resistor R11, having a timing capacitor C6 in shunt therewith, con- 6 nects the emitter circuit of unijunction U2 and section 82 to lead 30.

Lead 72 and the junction of the emitter circuit of U1 and section are connected to a calibration switch S1. Switch S1, during normal operation, connects lead 72 through an 82K resistor R12 to lead 78. If photocell section 80 approximates K, the potential at the emitter circuit of unijunction U1 tends toward the potential on lead 78, and unijunction U1 oscillates at a frequency between two and four times the AC. frequency applied to transformer T1 to apply gating pulses to the gate circ-uit of SCR1 at a frequency of two to four times the line frequency. The gating pulses, therefore, fire SCR1 each time lead 92 goes positive relative to lead 70. Lead 92 goes positive in relation to lead 70 at line frequency and since the gating pulse frequency is at least several times the line frequency, SCR1 will fire on each positive cycle applied to lead 92. Each time SCR1 fires, it of course operates relay 88. Relay 88 is held operated between gating pulses applied to SCR1 by capacitor C3 to prevent alarm A1 from operating. The alarm A1, therefore, does not function when the resistance of cell section 80 is in the neighborhood of 150K. The resistance of cell section 80 will, of course, vary in accordance with the light received thereby from lamp 28 and rod 40.

The switch S1 is arranged to connect a 250K calibrate resistor R13 to cell section 80 and the emitter circuit of U1 for enabling the resistance of cell section 80 to be calibrated and adjusted at 150K in the field. Resistor R13 is adjusted at the factory by connecting its variable arm to an accurate 150K resistance extending to lead 70, while photocell section 80 is disconnected. Rssistor R13 is adjusted, until transistor U1 first goes out of oscillation to release relay 88 and operate alarm A1. Photocell section 80 is then reconnected, as shown in FIG. 3, and the 150K resistor disconnected.

Thereafter the resistance of section 80 can be set at 150K in the field by simply operating switch S1 to connect the section 80 to resistor R13. The light intensity of lamp 28 is then controlled by adjusting resistor R3 to just drive unijunction U1 out of oscillation for operating alarm A1. The resistance of cell section 80 at that time corresponds to 150K. With section 80 at 150K, switch S1 is operated to reconnect section 80 to resistor R12 and unijunction U1 goes back into oscillation to turn off the alarm A1.

Since section 82 is substantially identical to section 80, and since its resistance is also set by the incident light applied to 80, its resistance will substantially follow section 80. At a light intensity sutficient to set section 80 at 150K, section 82 has a corresponding value and unijunction U2 goes into oscillation. However, if the incident light should thereafter decrease, such as occurs when lamp 28 fails, the voltage at the emitter of unijunction U2 will swing towards the potential on lead 30. Unijunction U2 terminates oscillation to hold SCR2 extinguished and release relay 90. Alarm A2 is therefore operated.

The section 10, together with assemblies 16 and 14, are installed intermediate a source of oil mist and the bearings to be lubricated thereby, as previously explained with circuit 76 interconnected with the lamp and photocell as shown in FIG. 3. Oil mist is generated in a desired ratio to air by the mist generator (not shown), until the lamp 28 and rod 40 have acquired a suitable stabilized coating. This may take at least several hours in some cases, since the output of the oil mist generator usually takes some time to reach its nominal value. The nominal value is usually determined by periodically assaying the oil output at the terminal end of the stream. The lamp and rod may actually acquire a stabilized coating within twenty minutes of the time the generator is supplying the nominal oil output. Once acquired, the coating remains substantially intact and may even be secured by applying the oil in mass to the lamp and rod and allowing the excess to run off. The thickness and opacity of the cOating will vary with the type of oil so that if it is desired to utilize the apparatus with one type of oil and subsequently with a second type of oil, a second stabilizing coating on the lamp and rod may be necessary.

With the mist generated in the desired ratio and a stabilized coating deposited, switch S1 is operated to connect resistor R13 to section 80 and the emitter circuit of transistor U1. If the oil to air ratio is high, such as .8 oz./hr./c.f.m., the resistance of section 80 is high and unijunction U1 oscillates accordingly. Resistor R3 is adjusted to raise the light intensity. The resistance of section 80, therefore, drops towards 150K and the emitter circuit of U1 swings negative toward the potential of lead 70. When the light intensity is just insuflicient to maintain transistor U1 in oscillation, SCRl remains extinguished and alarm A1 operates as explained. Cell section 80 is now at 150K with the optimum oil to air ratio being transmitted.

Switch S1 is then operated to disconnect resistor R13 from the emitter circuit of unijunction U1 and resistor R12 is connected thereto instead. With the 82K resistor R12 connected in series with cell 80 and cell 80 at a resistance of 150K, the potential at the emitter circuit of transistor U1 swings toward the potential on lead 78 and transistor U1 again goes into oscillation to terminate operation of alarm A1. The apparatus is. now effective to ascertain variations in the oil mist to air ratio.

If the oil mist to air ratio should thereafter fall, the light incident on cell 80 increases and the cell resistance falls below 150K. The emitter circuit of unijunction U1 swings negative towards the potential on lead 70 and unijunction U1 terminates oscillation to operate alarm A1 as previously explained. This signals a failure in the oil mist system.

It will be appreciated that the oil mist to air ratio .in each portion of the oil mist air stream is not a constant, but may vary in different portions of the stream due to the cycling of the generator and/or other factors. The light intensity transmitted to cell section 80 varies accordingly, and the alarm A1 is operated to indicate each variation or, if desired, appropriate time delays may be used so that alarm A1 signals an alarm condition, only if the oil mist to air ratio falls below the desired value for a sufficiently long period. If extreme sensitivity is desired, resistor R12 may be made adjustable and set at a value greater than 82K. A slight drop in the resistance of section 80 will, therefore, drive the emitter circuit of U1 sufficiently negative to hold SCRl extinguished and operate alarm Al for signalling this condition.

When the transmission of oil, for example, at .1 oz./ hr./c.f.m. is to be monitored, transmission at the desired ratio is initiated, as before described, until the lamp 28 and rod 40 are covered with a stabilized coating. Switch S1 is operated to connect resistor R13 to section 80 and the emitter circuit of U1. Since the light intensity would normally be high, resistor R3 is adjusted for maximum resistance and lamp 28 provides a low light intensity so that the resistance of section 80 is well above 150K and transistor U1 oscillates. Resistor R3 is then adjusted to increase the light intensity from lamp 28. The resistance of photocell 80 is, therefore, minimized until alarm A1 is actuated which, of course, occurs when section '80 approximates 150K. Switch S1 is now operated to connect R12 to the emitter of U1 instead of resistor R13. A subsequent decrease in the oil mist density causes the resistance of section 80 to fall below 150K and emitter of U1 then swings toward the potential of lead 70 to operate the alarm A1 and signal this condition.

If necessary, when operating under low oil to air ratios, the photocell assembly 16 may be adjustably positioned relative to lamp 28 to secure the desired sensitivity. Conversely, the lamp 28 may also be adjustably positioned relative to assembly 16.

Cell section 82 indicates either an excessively high oil ratio or a failure in the lamp 28. When the resistance of cell section 80 is set at 150K through adjustment of resistor R13, cell section 82 will, of course, follow the same resistance curve as section 80 as they are both exposed to similar light intensities. Section 82, therefore, also has a resistance approaching 150K. With the section 82 approximately 150K, transistor U2 is in oscillation to maintain alarm A2 off. When the light intensity falls, the resistance of section 82 rises and the emitter circuit of U2 swings towards the negative potential on lead 30. Unijunction U2, therefore, terminates oscillation. Alarm A2, therefore, operates in a manner previously explained to indicate this condition.

If desired, resistor R11 may also be made adjustable to lower its 300K nominal value. When the resistance of section 82 increases by a small amount due to a small increase in the oil to air ratios, the emitter circuit of U2 will be driven sufliciently negative to terminate oscillation and hold SCRZ extinguished. Alarm A2 is, therefore, operated to signal this condition.

While the lamp 28 and light transmitting rod 40 has been shown in the oil mist air stream for receiving light transmitted from lamp 28, it will be appreciated that the immersion of photocell directly in the stream for light reception, is not precluded.

The foregoing is a description of an improved method and apparatus for detecting variations in the density of oil mist particles in a fluid stream with the inventive concepts thereof set forth in the appended claims.

What is claimed is:

1. A method for use in calibrating apparatus used in detecting variations in the density of oil mist particles in an oil mist air stream, comprising the steps of locating a lamp and a light receiving device at spaced apart positions in the path of an oil mist stream carrying a known ratio of particles to air until a substantially constant coating of said particles is deposited on said lamp and device, and adusting the light intensity transmitted by said lamp through said stream to said device for operating a signal to indicate an initial desired light intensity transmitted through said stream and corresponding to said known ratio.

2. A method for use in detecting variations in oil mist particle density in an oil mist air stream, comprising the steps of locating a lamp at a position in the path of said stream, locating a light receiving device in the path of said stream and spaced from said lamp, moving said stream past said lamp and device until a substantially constant coating of said particles is deposited on said lamp and device, with the light transmitted by each stable coating being independent of fluctuations in the density of said oil particles in said stream, controlling the light intensity transmitted between said lamp and device after each stable coating is deposited and while a known ratio of oil mist particles to air are transported in said stream between said lamp and device to establish a reference light intensity received by said device, and thereafter detecting variations in the light intensity transmitted from said lamp to said device while said stream is moved between said lamp and device.

3. Apparatus for use in detecting variations in the density of an oil mist air stream, comprising a lamp having a light transmitting surface located in said stream, a light transparent device in said stream spaced from said lamp with both said surface and device having a substantially constant coating of oil and arranged so that light is transmitted from said lamp and surface to said device in a direction parallel to the longitudinal axis of said stream in inverse proportion to the oil particle density of said stream, each constant coating establishing a substantially invariant light transmission condition at said surface and device independent of fluctuations in the density of said oil mist air stream, a photocell external to said stream, means associated with said device for transmitting light received by said device to said photocell, and means controlled by said photocell in accordance with the light intensity transmitted thereto for signalling a variation in the light intensity received by said device. 7

4. In the apparatus claimed in claim 3, means for setting the impedance of said photocell at a known value, comprising a resistor, a switch for connecting said resistor to said photocell, and a unijunction having a bias electrode connected to the junction of said resistor and photocell and operated in one manner in response to the impedance of said photocell being at said known value.

5. Apparatus for detecting variations in density of an oil mist air stream, comprising a conduit through which said stream is passed, a lamp having a light transmitting surface in said conduit, a light prism in said conduit with said surface and prism carried by said conduit at spaced apart positions in said stream and arranged so that light is transmitted from said surface to said prism in a direction parallel to the longitudinal axis of said conduit, a substantially constant coating of oil deposited on said surface and prism with the light intensity transmitted by each coating thereafter being substanitally invariant and thereby independent of fluctuations in the density of said oil mist air stream, a photocell external to said conduit and having an impedance varying in accordance with the light intensity transmitted thereto, means establishing a light path between said prism and said photocell for transmitting light received by said prism to said photocell, and an electrical circuit controlled by said photocell providing a signal output indicating a variation in the light intensity transmitted through said stream to said prism and from said prism to said photocell.

6. The apparatus claimed in claim in which said photocell comprises two independent sections, said electrical circuit being individual to one of said sections for providing a signal output in response to an impedance of said one section varying in one direction, and another electrical circuit individual to the other section for providing a signal output in response to the impedance of said other section varying in the opposite direction from said one direction.

7. The apparatus claimed in claim 5 in which said means establishing a light path between said prism and photocell comprises a glass rod with said prism being formed at one end of said rod in said stream, and means supporting said photocell adjacent the other end of said rod external to said stream with said photocell supporting means comprising a heat insulating standard, a heat radiator carried by said standard, and a second heat insulating standard carried by said radiator for spacing said photocell from said stream a distance providing sufiicient light transmission to control said photocell and sufficient heat loss between said stream and photocell to prevent temperature variations of said stream from affecting said photocell.

8. For use in calibrating oil mist density detection apparatus of the type including a lamp for transmitting light through an oil mist air stream to a photocell located remote from said lamp with the impedance of said photocell varying in accordance with the light intensity transmitted through said stream, the improvement comprising, a resistor of known value connected in series with said photocell, an oscillator circuit including a unijunction with a control electrode connected between said resistor and photocell and arranged to terminate oscillation in response to the impedance of said photocell having a known value, an SCR having a control electrode connected to the output of said unijunction for firing said SCR in response to each oscillation generated by said oscillator circuit, a signal operated in response to the failure of said SCR to fire within a predetermined time interval to indicate said oscillator circuit has terminated oscillation, means for varying the light transmitted through said stream to said cell while a known ratio of oil particles are carried by said stream for varying the impedance of said cell until said oscillator circuit terminates oscillation whereby said signal is operated to indicate the impedance of said photocell has said known value.

9. In the improvement claimed in claim 8, a secono resistor having a known value, means for disconnecting said photocell and oscillator circuit from said first resistor and for connecting said photocell in series with said second resistor with said unijunction control electrode connected between said photocell and second resistor to thereby initiate oscillation of said oscillator circuit and terminate operation of said signal in response to said photocell having said known impedance, whereafter said signal is operated in response to a variation in the impedance of said photocell from said known impedance.

10. Apparatus for use in detecting a variation in the density of an oil mist air stream, comprising a conduit through which said stream and mist are passed, a lamp located in said stream, a light transparent rod in said stream spaced from said lamp with said lamp and rod arranged so that light is transmitted from said lamp to said rod in a direction parallel to the longitudinal axis of said stream and light received by said rod is transmitted external to said stream, a dual section photocell external to said stream and associated with said rod for receiving light transmitted through said stream to said rod with the resistance of each section varying in accordance with the light intensity transmitted thereto by said rod, an oscillator circuit for each section of said cell with each oscillator circuit having a unijunction normally generating pulses of a respective frequency, a pair of alarm circuits, a silicon-controlled rectifier for each oscillator with each rectifier controlled by the oscillations generated by the respective unijunction for maintaining said alarms deenergized only if the resistance of each section remains within predetermined limits whereby one of said rectifiers enables energization of the respective alarm in response to resistance of the respective cell falling below a predetermined value and the other rectifier enables energization of the respective alarm in response to the resistance of the respective cell rising above a predetermined value.

11. Apparatus for use in detecting variations in the density of oil mist particles carried in an air stream having a lamp located in said stream for transmitting light in a direction parallel to the longitudinal axis of said stream to a transparent rod arranged to in turn transmit said light in inverse proportion to the density of said stream to a dual section photocell external to said stream with the resistance of each section varying in accordance with the light intensity transmitted by said rod from said stream and lamp, the improvement comprising a respective unijunction arranged in a respective oscillator circuit for each photocell section with each unijunction under control of the respective section for generating gating pulses of a respective f requency if the impedance of the respective section approaches a predetermined value, a pair of alarms, a silicon-controlled rectifier for each alarm circuit and unijunction with each rectifier controlled by the gating pulses generated by a respective unijunction for controlling the respective alarms in one manner, a resistor having a selected resistance, means for connecting said resistor to one of said cell sections, means for adjusting the light intensity transmitted from said lamp with said stream carrying a known ratio of oil to air to control the impedance of both cell sections accordingly, whereby the impedance of said sections is adjusted to said predetermined value as indicated by operation of one of said alarms in response to the termination of said gating pulses by one of said oscillators, another resistor, and means for thereafter disconnecting said selected resistor and connecting said one cell section to said other resistor for controlling the respective os cillator to generate gating pulses of said predetermined frequency to disable the respective alarm only as long as known value.

References Cited UNITED STATES PATENTS Katzman 8814 Albert 250218 X Souther 250218 X Doy-le 307--88.5

12 3,206,612 9/ 1965 Swanekamp et a1. 307-885 3,268,734 8/1966 Bjorn 250218 3,308,300 3/1967 Kadivnik 250218 5 lRALP-H G. NILSON, Primary Examiner.

T. N. GRIGSBY, Assist ant Examiner. 

